Future Climate Effects on Thermal Stratification in the Wachusett Reservoir

A two-dimensional hydrodynamic and water quality model, CE-QUAL-W2, was used to simulate the effects of increasing future air temperatures on water temperature, stratification timing and duration, as well as changes in winter ice cover in the Wachusett Reservoir, a major drinking water supply for metropolitan Boston, Mass. Historic model years 2003–2012 provided a framework to evaluate the sensitivity of reservoir thermal processes to future synthetic climate scenarios over a 100-year span. Average epilimnion and hypolimnion temperatures increased by about 12 and 7%, respectively, after 100 years of increasing air temperatures. Stratification duration increased by one to two weeks, beginning earlier and ending later than the historical stratification period. Additionally, the average number of days with ice cover decreased 18–57% by the end of all scenarios. Results provide insight into the sensitivity of Wachusett Reservoir water temperatures and the potential effects of increasing air temperatures caused by climate change.